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我正在为我的 JSF 应用程序使用视图范围的托管 bean。由于需要对视图范围的 bean 进行序列化，因此我实现了 Serializable。但问题在于EntityManager。我尝试使用瞬态关键字绕过它，但出现以下异常。

我使用了以下 bean 文件：

@ManagedBean
@ViewScoped
public class StatusBean2 implements Serializable  {

    /**
     * 
     */
    private static final long serialVersionUID = -7528998562821856315L;
    private transient EntityManager em;

    public StatusBean2() {
        EntityManagerFactory emf = Persistence
                .createEntityManagerFactory("FreeBird");
        em = emf.createEntityManager();
        FacesContext context = FacesContext.getCurrentInstance();
        HttpSession session = (HttpSession) context.getExternalContext()
                .getSession(true);
        int toIndex = 5;
       session.setAttribute("toIndex", toIndex);

    }
    public List<Status> getStatusList() {
        FacesContext context = FacesContext.getCurrentInstance();
        HttpSession session = (HttpSession) context.getExternalContext()
                .getSession(true);
        User user = (User) session.getAttribute("userdet");
        Query query = em.createQuery("SELECT s FROM Status s WHERE s.email='"//  line no 49
                + user.getEmail() + "' ORDER BY s.timeMillis desc",
                Status.class);
        List<Status> results = query.getResultList();
        Query query1 = em.createQuery("SELECT f FROM Friend f WHERE f.email='"
                + user.getEmail() + "'", Friend.class);
        List<Friend> results1 = query1.getResultList();
        Iterator<Friend> it = results1.listIterator();
        while (it.hasNext()) {
            String email = it.next().getFriendEmail();
            Query query2 = em.createQuery(
                    "SELECT s FROM Status s WHERE s.email='" + email
                            + "' ORDER BY s.timeMillis desc", Status.class);
            List<Status> results2 = query2.getResultList();
            results.addAll(results2);

        }
        Collections.sort(results);

        int toIndex = (int) session.getAttribute("toIndex");
        List<Status> subList = results.subList(0, toIndex);

        return subList;

    }
}

当我在 EntityManager 上瞬态时遇到的异常如下：

javax.el.ELException: /Home.xhtml @458,24 items="#{statusBean2.statusList}": Error reading 'statusList' on type com.bean.StatusBean2
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:111)
    at com.sun.faces.facelets.tag.jstl.core.ForEachHandler.apply(ForEachHandler.java:158)
    at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:94)
    at javax.faces.view.facelets.DelegatingMetaTagHandler.applyNextHandler(DelegatingMetaTagHandler.java:131)
    at com.sun.faces.facelets.tag.jsf.ComponentTagHandlerDelegateImpl.apply(ComponentTagHandlerDelegateImpl.java:162)
    at javax.faces.view.facelets.DelegatingMetaTagHandler.apply(DelegatingMetaTagHandler.java:114)
    at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:94)
    at javax.faces.view.facelets.DelegatingMetaTagHandler.applyNextHandler(DelegatingMetaTagHandler.java:131)
    at com.sun.faces.facelets.tag.jsf.ComponentTagHandlerDelegateImpl.apply(ComponentTagHandlerDelegateImpl.java:162)
    at javax.faces.view.facelets.DelegatingMetaTagHandler.apply(DelegatingMetaTagHandler.java:114)
    at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:94)
    at com.sun.faces.facelets.compiler.NamespaceHandler.apply(NamespaceHandler.java:89)
    at javax.faces.view.facelets.CompositeFaceletHandler.apply(CompositeFaceletHandler.java:94)
    at com.sun.faces.facelets.compiler.EncodingHandler.apply(EncodingHandler.java:79)
    at com.sun.faces.facelets.impl.DefaultFacelet.apply(DefaultFacelet.java:148)
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.buildView(FaceletViewHandlingStrategy.java:711)
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:96)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
    at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:135)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:309)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:79)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1001)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:579)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
    at com.bean.StatusBean2.getStatusList(StatusBean2.java:49)
    at sun.reflect.GeneratedMethodAccessor78.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at javax.el.BeanELResolver.getValue(BeanELResolver.java:87)
    at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:67)
    at com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:71)
    at org.apache.el.parser.AstValue.getValue(AstValue.java:169)
    at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:106)
4

1 回答 1

0

反序列化对象时不调用构造函数，因此该transient字段为 left null。

您需要延迟初始化该字段：

@ManagedBean
@ViewScoped
public class StatusBean2 implements Serializable  {
    private static final long serialVersionUID = -7528998562821856315L;
    private transient EntityManager em;
    private static final EntityManagerFactory emf = Persistence.createEntityManagerFactory("FreeBird");

    public StatusBean2() {
        FacesContext context = FacesContext.getCurrentInstance();
        HttpSession session = (HttpSession) context.getExternalContext()
                .getSession(true);
        int toIndex = 5;
        session.setAttribute("toIndex", toIndex);   
    }

    private EntityManager em() {
        if(em == null)
            em = emf.createEntityManager();
        return em;
    }

    public List<Status> getStatusList() {
        FacesContext context = FacesContext.getCurrentInstance();
        HttpSession session = (HttpSession) context.getExternalContext()
                .getSession(true);
        User user = (User) session.getAttribute("userdet");
        Query query = em().createQuery("SELECT s FROM Status s WHERE s.email='"//  line no 49
                + user.getEmail() + "' ORDER BY s.timeMillis desc", Status.class);
        List<Status> results = query.getResultList();
        Query query1 = em().createQuery("SELECT f FROM Friend f WHERE f.email='"
                + user.getEmail() + "'", Friend.class);
        List<Friend> results1 = query1.getResultList();
        Iterator<Friend> it = results1.listIterator();
        while (it.hasNext()) {
            String email = it.next().getFriendEmail();
            Query query2 = em().createQuery(
                    "SELECT s FROM Status s WHERE s.email='" + email + 
                    "' ORDER BY s.timeMillis desc", Status.class);
            List<Status> results2 = query2.getResultList();
            results.addAll(results2);
        }
        Collections.sort(results);
        int toIndex = (int) session.getAttribute("toIndex");
        List<Status> subList = results.subList(0, toIndex);
        return subList;
    }
}
于 2013-05-01T22:15:47.317 回答